Background image is blurry
As workaround, you could get away with Import Image as Plane Addon which creates a simple plane that you can use as reference. It actually also creates a texture shader for which you can use interpolation as closest in the shader texture node.



If you still want to be able to position it in front and change the alpha not as convenient as the background image but, you can add transparent and a mix shader. And disable selection mode to let you select object located behind it.